JP2024505841A - Negative electrode active material, negative electrode containing the same, secondary battery containing the same, and method for producing negative electrode active material - Google Patents

Abstract

The present invention relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the same, and a method for producing the negative electrode active material.

Description

This application is based on Korean Patent Application No. 10-2021-0107525 filed with the Korean Patent Office on August 13, 2021 and Korean Patent Application No. 10 filed with the Korean Patent Office on January 20, 2022. 2022-0008564, the entire contents of which are incorporated herein.

The present invention relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the same, and a method for producing the negative electrode active material.

In recent years, with the rapid spread of electronic devices that use batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries, which are small and lightweight but have relatively high capacity, is rapidly increasing. . In particular, lithium secondary batteries are lightweight and have high energy density, and are attracting attention as a driving power source for portable devices. For this reason, active research and development efforts are being made to improve the performance of lithium secondary batteries.

Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. Furthermore, active material layers containing a positive electrode active material and a negative electrode active material, respectively, can be formed on the current collectors of the positive electrode and the negative electrode. Generally, a lithium-containing metal oxide such as LiCoO ₂ or LiMn ₂ O ₄ is used as a positive electrode active material for the positive electrode, and a carbon-based active material or a silicon-based active material that does not contain lithium is used as a negative electrode active material for the negative electrode. It is being

Among negative electrode active materials, silicon-based active materials are attracting attention because they have higher capacity and excellent high-speed charging characteristics than carbon-based active materials. However, silicon-based active materials have a drawback that initial efficiency is low because the volume expands/contracts to a large degree in response to charging and discharging, and has a large irreversible capacity.

On the other hand, among silicon-based active materials, silicon-based oxides, specifically silicon-based oxides represented by _SiO It has the advantage that the degree of expansion/contraction of volume in response to charging and discharging is low. However, silicon-based oxides still have the disadvantage of lower initial efficiency due to the presence of irreversible capacitance.

In connection with this, research has continued in an attempt to reduce irreversible capacity and improve initial efficiency by doping or inserting metals such as Li, Al, and Mg into silicon-based oxides. However, in the case of a negative electrode slurry containing a metal-doped silicon-based oxide as a negative electrode active material, the metal oxide formed by doping the metal reacts with moisture to increase the pH of the negative electrode slurry and change its viscosity. Therefore, there is a problem that the state of the manufactured negative electrode becomes poor and the charge/discharge efficiency of the negative electrode decreases.

Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of a negative electrode slurry containing a silicon-based oxide and thereby improve the charge/discharge efficiency of the manufactured negative electrode.

Korean Patent No. 10-0794192 relates to a method of manufacturing a carbon-coated silicon-graphite composite negative electrode material for a lithium secondary battery and a method of manufacturing a secondary battery including the same, and solves the above-mentioned problems. has its limits.

Korean Registered Patent No. 10-0794192

The present invention relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the same, and a method for producing the negative electrode active material.

One embodiment of the present invention provides silicon-based particles containing SiO _x (0<x<2) and a Li compound and provided with a carbon layer on at least part of the surface; and at least part of the silicon-based particles. When analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to O (F/O ratio) is 0.45 or more, and the atomic ratio of F to C (F/O ratio) is 0.45 or more. /C ratio) is 0.5 or less.

One embodiment of the present invention provides a step of forming silicon-based particles containing SiO _x (0<x<2) and a Li compound and provided with a carbon layer on at least a portion of the surface; Provided is a method for producing the negative electrode active material, which includes the step of reacting a solution to form a layer containing LiF on at least a portion of the silicon-based particles.

One embodiment of the present invention provides a negative electrode including the negative electrode active material.

One embodiment of the present invention provides a secondary battery including the negative electrode.

A negative electrode active material according to an embodiment of the present invention effectively removes lithium by-products formed when silicon-based particles are doped with Li to improve water-based processability, and includes a layer containing LiF on the silicon-based particles. This allows it to act as an artificial SEI layer and improve life performance. In addition, the atomic ratio of F to O (F/O ratio) on the particle surface is 0.45 or more, and the atomic ratio of F to C (F/C ratio) is 0.5 or less to improve water-based processability. can be significantly improved.

Therefore, a negative electrode including a negative active material according to an embodiment of the present invention and a secondary battery including the negative electrode have the advantage that discharge capacity, initial efficiency, resistance performance, and/or life characteristics of the battery are improved.

The present specification will be explained in more detail below.

In this specification, when a certain part is said to "include" a certain component, this does not mean that the other component is excluded, unless there is a specific statement to the contrary, but it does not mean that the other component may be further included. means.

In this specification, when a member is referred to as being "on" another member, this refers not only to the case where the member is in contact with the other member, but also when the member is located between the two members or on the other member. This also includes cases where members are present.

The terms and words used herein are not to be construed as limited to their ordinary or dictionary meanings, and the inventors have used the terminology to best describe their invention. In accordance with the principle that the concept can be appropriately defined, the meaning and concept should be interpreted in accordance with the technical idea of the present invention.

As used herein, the singular terminology includes the plural terminology unless the context clearly dictates otherwise.

In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis, and the X-ray diffraction analysis is performed using an XRD (X-ray diffraction) analysis device (product name: D4 -endervor, manufactured by Bruker), and in addition to the above-mentioned equipment, equipment used in the industry can be appropriately employed.

In this specification, the presence or absence of an element in the negative electrode active material and the content of the element can be confirmed by ICP analysis, and ICP analysis is performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300). It can be carried out.

In this specification, the average particle size (D ₅₀ ) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of a particle size distribution diagram) of particles. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes in the submicron range to several millimeters, and can provide results with high reproducibility and high resolution.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified into various forms, and the scope of the present invention is not limited to the embodiments described below.

<Negative electrode active material>
One embodiment of the present invention provides silicon-based particles containing SiO _x (0<x<2) and a Li compound and provided with a carbon layer on at least part of the surface; and at least part of the silicon-based particles. When analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to O (F/O ratio) is 0.45 or more, and the atomic ratio of F to C (F/O ratio) is 0.45 or more. /C ratio) is 0.5 or less.

A negative active material according to an embodiment of the present invention includes silicon-based particles. The silicon-based particles include SiO _x (0<x<2) and a Li compound, and may include a carbon layer on at least a portion of the surface.

The SiO _x (0<x<2) may correspond to a matrix within the silicon-based particles. The SiO _x (0<x<2) may include Si and SiO ₂ , and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO _x (0<x<2). When the silicon-based particles include the SiO _x (0<x<2), the discharge capacity of the secondary battery can be improved.

In one embodiment of the present invention, the silicon-based particles may include a Li compound.

The Li compound may correspond to a matrix within the silicon-based particles. The Li compound may exist in the silicon-based particles in the form of at least one of lithium atoms, lithium silicate, lithium silicide, and lithium oxide. When the silicon-based particles contain a Li compound, the initial efficiency is improved.

The Li compound may be doped into the silicon-based particles and distributed on the surface and/or inside the silicon-based particles. The Li compound is distributed on the surface and/or inside of the silicon-based particles, and can control the expansion/contraction of the volume of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. can. In addition, the Li compound may be included to reduce the proportion of an irreversible phase (eg, SiO ₂ ) in the silicon-based oxide particles, thereby increasing the efficiency of the active material.

In one embodiment of the invention, the Li compound may be present in the form of lithium silicate. The lithium silicate is represented by Li _a Si _b O _c (2≦a≦4, 0<b≦2, 2≦c≦5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. . The crystalline lithium silicate may exist in the silicon-based particles in the form of at least one lithium silicate selected from the group consisting of Li ₂ SiO ₃ , Li ₄ SiO ₄ , and Li ₂ Si ₂ O ₅ . Often, amorphous lithium silicate may consist of a complex in the form of Li _a Si _b O _c (2≦a≦4, 0<b≦2, 2≦c≦5), and the above-mentioned form but not limited to.

In one embodiment of the present invention, Li may be included in an amount of 0.1 parts by weight to 40 parts by weight, or 0.1 parts by weight to 25 parts by weight, based on a total of 100 parts by weight of the negative active material. Specifically, it may be contained in an amount of 1 part by weight to 25 parts by weight, and more specifically, in an amount of 2 parts by weight to 20 parts by weight. There is a problem that as the Li content increases, the initial efficiency increases but the discharge capacity decreases, so if the above range is satisfied, suitable discharge capacity and initial efficiency can be achieved.

The content of the Li element can be confirmed by ICP analysis. Specifically, after a certain amount (about 0.01 g) of the negative electrode active material is collected, it is transferred to a platinum crucible, and nitric acid, hydrofluoric acid, and sulfuric acid are added thereto to completely decompose it on a hot plate. Then, using an inductively coupled plasma emission spectrometer (ICPAES, Perkin-Elmer 7300), measure the intensity of the standard solution prepared using the standard solution (5 mg/kg) at the characteristic wavelength of the element to be analyzed. Create a standard calibration curve. After that, the pretreated sample solution and blank sample are introduced into the device, the intensity of each is measured to calculate the actual intensity, and the concentration of each component is calculated by comparing it with the calibration curve created above. The content of the elements in the produced negative electrode active material can be analyzed by converting so that the total sum becomes the theoretical value.

In one embodiment of the invention, the silicon-based particles may include additional metal atoms. The metal atoms may exist in the silicon-based particles in the form of at least one of metal atoms, metal silicate, metal silicide, and metal oxide. The metal atom may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Accordingly, the initial efficiency of the negative electrode active material can be improved.

The silicon-based particles according to one embodiment of the present invention are provided with a carbon layer on at least a portion of the surface. At this time, the carbon layer may be in the form of covering at least a part of the surface, that is, partially covering the surface of the particle, or covering the entire surface of the particle. The carbon layer imparts conductivity to the negative electrode active material, and the initial efficiency, life characteristics, and capacity characteristics of the secondary battery can be improved.

In one embodiment of the invention, the carbon layer includes an amorphous phase.

In one embodiment of the invention, the carbon layer includes amorphous carbon.

Moreover, the carbon layer may further contain crystalline carbon.

The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotubes, and graphene.

The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress expansion of the silicon-based particles. The amorphous carbon is a carbon-based material formed using at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a hydrocarbon as a source of chemical vapor deposition. Good too.

The other carbonized organic substance may be a carbonized organic substance selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

The hydrocarbons may be substituted or unsubstituted aliphatic or alicyclic hydrocarbons, substituted or unsubstituted aromatic hydrocarbons. The aliphatic or alicyclic hydrocarbon of said substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. good. The aromatic hydrocarbons of the substituted or unsubstituted aromatic hydrocarbons include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumaron, pyridine, anthracene, or phenanthrene. Examples include.

In one embodiment of the present invention, the carbon layer is 0.1 parts by weight to 50 parts by weight, 0.1 parts by weight to 30 parts by weight, or 0.1 parts by weight based on a total of 100 parts by weight of the negative electrode active material. % to 20 parts by weight. More specifically, it may be included in an amount of 0.5 parts to 15 parts by weight, 1 part to 10 parts by weight, or 1 part to 5 parts by weight. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and/or life of the battery is reduced. It has the effect of being improved.

Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

A negative active material according to an embodiment of the present invention includes a layer containing LiF provided on at least a portion of the silicon-based particles.

The layer containing LiF may be in the form of coating at least a portion of a silicon-based particle having a carbon layer on its surface. That is, the layer containing LiF may be partially coated on the surface of the particle, or may be coated on the entire surface of the particle. Examples of the shape of the layer containing LiF include an island type or a thin film type, but the shape of the layer containing LiF is not limited thereto.

The layer containing LiF may be provided on at least a portion of the carbon layer. That is, the layer containing LiF may be coated adjacently on the carbon layer and provided in the form of particles containing SiO _x (0<x<2) and Li compound-carbon layer-layer containing LiF. good.

The layer containing LiF may be provided on a region in the surface of the particle containing the SiO _x (0<x<2) and the Li compound that is not provided with a carbon layer. _That is, the layer containing LiF is coated adjacently on the particles containing SiO _x (0<x<2) and a Li compound, and the layer containing LiF It may be provided in the form of a layer containing.

The layer containing LiF may be a LiF layer made of LiF. Alternatively, the layer containing LiF mainly contains LiF, and may also contain a trace amount of impurities such as a lithium compound in addition to LiF.

Whether or not the negative electrode active material contains LiF can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron analysis (XPS).

In one embodiment of the present invention, the layer containing LiF may be formed by a reaction between HF and one or more lithium compounds selected from the group consisting of Li ₂ O, LiOH, and Li ₂ CO ₃ . The formed LiF is uniformly formed on the surface of the particles and preferentially forms a layer on the surface (upper part) of the lithium byproduct to easily block the reaction between water and lithium compounds, and when the battery is operated, artificial SEI It has the effect of improving life performance by acting as an artificial SEI layer.

Specifically, the layer containing LiF may be formed by acid-treating a lithium compound, that is, a lithium byproduct, remaining near the surface of the silicon-based particles or carbon layer with HF after manufacturing the silicon-based particles. good.

In one embodiment of the present invention, the lithium compound may be one or more selected from the group consisting of Li ₂ O, LiOH, and Li ₂ CO ₃ .

When the lithium compound and HF react, a layer containing LiF may be generated by one or more reactions among the following formulas (1) to (3).
(1) LiOH+HF→LiF+ _H2O
(2) _Li2O +2HF→2LiF+ _H2O
( 3) _Li2CO3 + _2HF →2LiF+ _H2CO3

Since the layer containing LiF generated as described above does not dissolve well in water, it can efficiently passivate silicon-based particles in an aqueous slurry, and Li compounds contained in silicon-based particles are eluted. This has the effect of preventing water-based process from occurring and improving aqueous processability. In addition, the layer containing LiF acts as an artificial SEI layer during operation of the battery, thereby improving the life performance of the battery.

In the present invention, the content and atomic ratio of elements on the surface of the negative electrode active material can be confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)).

Specifically, after obtaining a survey scan spectrum and a narrow scan spectrum for each sample, the survey scan spectrum and narrow scan spectrum were obtained while performing a depth profile. Obtainable. The depth profile can be performed for up to 3000 seconds using monatomic Ar ions, and the measurement and data processing conditions are as follows.

-X-ray source: Monochromated Al K α (1486.6eV)
-X-ray spot size: 400μm
- Sputtering gun: Monatomic Ar (energy: 1000eV, current: low, raster width: 2mm)
-Etching rate: 0.09nm/s for Ta ₂ O ₅
- Operation Mode: CAE (Constant Analyzer Energy) mode
-Survey scan: pass energy 200eV, energy step 1eV
-Narrow scan: scanned mode, pass energy 50eV, energy step 0.1eV
-Charge compensation: flood gun off
-SF:Al THERMO1
-ECF:TPP-2M
-BG subtraction: Shirley

In one embodiment of the present invention, the depth profile of the X-ray photoelectron spectroscopy (XPS) is 0.09 nm/s under an X-ray source of Monochromated Al K α. Measurements can be made for up to 3000 seconds.

In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to O (F/O ratio) is 0.45 or more. . Specifically, it may be 0.48 or more, 0.55 or more, 0.6 or more, or 0.7 or more, 20 or less, 15 or less, 10 or less, 5 or less, 3 or less, 2 or less, 1. It may be 5 or less, or 1.2 or less.

In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to C (F/C ratio) is 0.5 or less. . Specifically, it may be 0.4 or less, 0.3 or less, 0.25 or less, or 0.22 or less, and it may be more than 0, 0.05 or more, 0.08 or more, or 0.1 or more. You can.

When the above F/O ratio and F/C ratio are satisfied, the LiF coating becomes uniform on the silicon particles, the particle coverage increases, and the passivation effect increases. lithium by-products can be easily removed and exposure of lithium by-products can be easily prevented, thereby effectively improving water-based processability and improving battery capacity, efficiency, and/or life performance. effective.

On the other hand, when the negative electrode active material does not satisfy the F/O ratio and/or the F/C ratio, the particle coverage is low and LiF is partially formed thickly. However, since passivation of particles is not easy and lithium by-products are easily exposed, aqueous processing properties are poor, and battery characteristics are also deteriorated.

Therefore, optimal battery characteristics can be exhibited when the F/O ratio and F/C ratio of the negative electrode active material satisfy the above ranges.

In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), F may be 0.1 at% to 0.3 at% based on 100 at% of the total elements.

In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), O is 5 at% to 14 at% or 8 at% to 13.5 at% based on 100 at% of the total elements. You can.

In one embodiment of the present invention, when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), C may be 50 at% to 65 at% or 55 at% to 61 at% based on 100 at% of the total elements. good.

In one embodiment of the present invention, when analyzing the negative electrode active material by X-ray photoelectron spectroscopy (XPS), Si may be 6 at% to 8 at% or 7 at% to 8 at% based on 100 at% of the total elements. good.

In one embodiment of the present invention, when analyzing the negative electrode active material by X-ray photoelectron spectroscopy (XPS), Li may be 10 at% to 25 at% or 10 at% to 20 at% based on 100 at% of the total elements. good.

In one embodiment of the present invention, the layer containing LiF may be included in an amount of 0.5 parts by weight or more and 5 parts by weight or less based on a total of 100 parts by weight of the negative electrode active material. Specifically, it may be contained in an amount of 0.7 parts by weight or more, 0.8 parts by weight or more, or 4 parts by weight or less, 3 parts by weight or less, or 2.5 parts by weight or less.

In one embodiment of the present invention, LiF may be included in an amount of 0.5 parts by weight or more and 5 parts by weight or less based on a total of 100 parts by weight of the negative electrode active material. Specifically, it may be contained in an amount of 0.7 parts by weight or more, 0.8 parts by weight or more, or 4 parts by weight or less, 3 parts by weight or less, or 2.5 parts by weight or less.

When the LiF content satisfies the above range, a layer is sufficiently formed on the surface (upper part) of the lithium by-product to easily block the reaction between water and the lithium compound, forming an artificial SEI layer during battery operation. This has the effect of improving life performance by acting as a

On the other hand, when LiF is contained in an amount less than 0.5 parts by weight, the LiF content is too small and the particles cannot be properly passivated, and the lithium by-products react with moisture, resulting in poor water-based processability. There is a problem with becoming.

In one embodiment of the present invention, a lithium compound (lithium byproduct) may be present between the silicon-based particles and the layer containing LiF.

Specifically, the lithium compound (byproduct) may refer to a lithium compound remaining near the surface of the silicon-based particles or the carbon layer after the silicon-based particles are manufactured. As described above, even after the acid treatment step, lithium by-products that have not reacted with the acid may remain.

The lithium compound may include one or more selected from the group consisting of Li ₂ O, LiOH, and Li ₂ CO ₃ . As in the reaction described above, the lithium compound and HF react to form a layer containing LiF, and the lithium compound (lithium by-product) generated by the lithium that remained without reacting with HF reacts with silicon-based particles and LiF. It may exist between a layer containing.

Whether or not a lithium compound exists between the silicon-based particles and the layer containing LiF can be confirmed by X-ray diffraction analysis (XRD) or X-ray photoelectron spectroscopy (XPS).

The lithium compound (byproduct) may be included in an amount of 5 parts by weight or less based on a total of 100 parts by weight of the negative active material. Specifically, it may be included in an amount of 0.01 parts by weight to 5 parts by weight, 0.05 parts by weight to 2 parts by weight, or 0.1 parts by weight to 1 part by weight. More specifically, it may be included in an amount of 0.1 part by weight to 0.8 part by weight, or 0.1 part by weight to 0.5 part by weight. When the content of the lithium byproduct satisfies the above range, side reactions in the slurry can be reduced, viscosity change can be reduced, and aqueous processing properties can be improved. On the other hand, if the content of lithium byproducts is higher than the above range, the slurry becomes basic when formed, which may cause side reactions or change the viscosity, causing problems in water-based processing. .

The content of the lithium compound (byproduct) is determined by measuring the amount of the HCl solution in a specific period where the pH changes during the titration process of the aqueous solution containing the negative electrode active material with an HCl solution using a titrator. Able to calculate quantities.

The average particle diameter (D ₅₀ ) of the negative electrode active material may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. . When the above range is satisfied, the active material is structurally stabilized during charging and discharging, and the problem of volume expansion/contraction level being increased due to excessively large particle size is prevented, and the particle size is not excessively low. This can prevent the problem of decreasing initial efficiency.

<Method for manufacturing negative electrode active material>
One embodiment of the present invention provides a step of forming silicon-based particles containing SiO _x (0<x<2) and a Li compound and provided with a carbon layer on at least a portion of the surface; Provided is a method for producing the negative electrode active material, which includes the step of reacting a solution to form a layer containing LiF on at least a portion of the silicon-based particles.

The silicon-based particles are produced by heating Si powder and SiO ₂ powder in a vacuum to vaporize them, and then depositing the vaporized gas mixture to form preliminary particles; forming a carbon layer on the surface of the formed preliminary particles; and a step of mixing the preliminary particles on which the carbon layer is formed with Li powder and then heat-treating the mixture.

Specifically, the mixed powder of Si powder and SiO ₂ powder may be heat-treated at 1300° C. to 1800° C., 1400° C. to 1800° C., or 1400° C. to 1600° C. under vacuum.

The pre-particles formed may have the form of SiO.

The carbon layer may be formed by using a chemical vapor deposition (CVD) method using hydrocarbon gas, or by carbonizing a material serving as a carbon source.

Specifically, the formed preliminary particles may be introduced into a reactor and then subjected to chemical vapor deposition (CVD) using hydrocarbon gas at 600 to 1200°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900°C to 1000°C.

The heat treatment step after mixing the preliminary particles on which the carbon layer is formed and the Li powder may be performed at 700° C. to 900° C. for 4 hours to 6 hours, and specifically, may be performed at 800° C. for 5 hours. good.

The silicon-based particles may include Li silicate, Li silicide, Li oxide, or the like as the Li compound described above.

The particle size of the silicon-based particles may be controlled by methods such as, but not limited to, a ball mill, a jet mill, or air classification.

A lithium compound (lithium byproduct) is provided on at least a portion of the silicon-based particle surface provided with the carbon layer as described above. Specifically, in the process of forming preliminary particles containing the SiO _x (0<x<2), forming a carbon layer on the preliminary particles, and doping with Li to manufacture the silicon-based particles, A lithium compound, that is, a lithium byproduct formed by unreacted lithium, remains near the surface of the silicon-based particles.

In one embodiment of the present invention, the method for producing the negative electrode active material includes the step of reacting the silicon-based particles with an HF solution to form a layer containing LiF on at least a portion of the silicon-based particles.

Specifically, in order to suppress side reactions caused by the unreacted lithium compound, a step of forming a layer containing LiF on at least a portion of the silicon-based particles may be performed.

The formed LiF preferentially forms a layer on the surface (top) of the lithium byproduct to easily block the reaction between water and lithium compounds, and acts as an artificial SEI layer when the battery is operated. This has the effect of improving life performance.

In one embodiment of the present invention, the step of forming a layer containing LiF on at least a portion of the silicon-based particles by reacting the silicon-based particles with an HF solution may include forming a layer containing LiF on at least a portion of the silicon-based particles. the lithium compound and the HF solution.

Specifically, the layer containing LiF may be formed by reacting a lithium compound provided on at least a portion of the silicon-based particles with an HF solution.

The layer containing LiF is formed by the reaction of HF with lithium compounds (Li ₂ O, LiOH, and Li ₂ CO ₃ ) caused by lithium that did not react with the preliminary particles (SiO) during the formation of the silicon-based particles described above. You can.

When the lithium compound and the HF solution react, a layer containing LiF may be generated by one or more reactions among the following formulas (1) to (3).
(1) LiOH+HF→LiF+ _H2O
(2) _Li2O +2HF→2LiF+ _H2O
( 3) _Li2CO3 + _2HF →2LiF+ _H2CO3

The HF solution may have a concentration of 0.03M to 0.3M, specifically 0.05M to 0.2M.

The silicon-based particles and the HF solution may be mixed in a weight ratio of 1:1 to 1:10, more specifically, in a weight ratio of 1:5 to 1:10.

After mixing the silicon-based particles and the HF solution, heat treatment may be performed at 200°C to 500°C, specifically, heat treatment may be performed at 250°C to 350°C.

When a layer containing LiF is formed by a chemical reaction between a lithium compound and HF as described above, LiF is uniformly formed on the surface of the particles, and the formed LiF is preferentially deposited on the surface (upper part) of the lithium byproduct. It forms a layer to easily block the reaction between water and lithium compounds, and acts as an artificial SEI layer when the battery is operated, thereby improving the life performance.

<Negative electrode>
A negative electrode according to an embodiment of the present invention may include the negative electrode active material described above.

Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder, a thickener, and/or a conductive material.

The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and/or a conductive material to at least one surface of a current collector, and drying and rolling the slurry.

The negative electrode slurry may further include an additional negative active material.

As the additional negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, and Si alloys. Metallic compounds that can be alloyed with _lithium , such as , _Sn alloy, or Al alloy; Metal oxides that can be doped and dedoped; or composites containing the metallic compound and carbonaceous material such as Si-C composites or Sn-C composites, and any one of these Or a mixture of two or more may be used. Moreover, a metal lithium thin film may be used as the negative electrode active material. Further, as the carbon material, either low crystalline carbon or high crystalline carbon may be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, and examples of high-crystalline carbon include amorphous, plate-like, scale-like, spherical, or fibrous natural graphite. Or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, meso-carbon microbeads, Phase pitches (Mesophase pitches) and high temperature calcined carbons such as petroleum or coal tar pitch derived cokes.

The additional negative electrode active material may be a carbon-based negative electrode active material.

In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material contained in the negative electrode slurry may be 10:90 to 90:10, specifically 10:90 to 50. :50 may be sufficient.

The negative electrode slurry may include a negative electrode slurry forming solvent. Specifically, the negative electrode slurry forming solvent is at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, in terms of facilitating the dispersion of components. May contain water.

The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. . Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

The binder may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate. ate), polyvinyl alcohol, carboxymethyl cellulose (CMC) , starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, poly It may contain at least one selected from the group consisting of polyacrylic acid and substances in which the hydrogens thereof are replaced with Li, Na, Ca, etc., and may also contain various copolymers thereof. But that's fine.

The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, such as graphite such as natural graphite or artificial graphite; acetylene black, Ketjen black, channel black, etc. Carbon black such as black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powder; Zinc oxide, titanic acid Conductive whiskers such as potassium; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may also be used.

The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and thickeners used in the present technical field may be appropriately employed.

<Secondary battery>
A secondary battery according to one embodiment of the present invention may include the negative electrode according to one embodiment described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof will be omitted.

The positive electrode may include a positive electrode current collector, and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, such as stainless steel, aluminum, nickel, titanium, fired carbon, or Aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. may also be used. Further, the positive electrode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. . For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, and nonwoven body.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; LiFe ₃ O ₄ Lithium iron oxides such as; chemical formula Li _1+c1 Mn _2-c1 O ₄ (0≦c1≦0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxides (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ ; chemical formula LiNi _1-c2 M _c2 O ₂ (where M is Co, Mn, Al, Cu, Fe , Mg, B, and Ga, and satisfies 0.01≦c2≦0.3); chemical formula: LiMn _2-c3 M _c3 O ₂ (here, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), or Li ₂ Lithium manganese composite oxide represented by Mn ₃ MO ₈ (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or a part of Li in the chemical formula Examples include, but are not limited to, LiMn ₂ O ₄ in which is substituted with an alkaline earth metal ion. The positive electrode may be made of Li-metal.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular restrictions as long as it does not cause chemical changes and has electronic conductivity in the constructed battery. be. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; copper, nickel, Examples include metal powders or metal fibers such as aluminum and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. One kind alone or a mixture of two or more kinds may be used.

In addition, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl Cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among them, one type or a mixture of two or more types may be used.

The separator separates the negative and positive electrodes and provides a passage for lithium ions to move.If it is normally used as a separator in secondary batteries, it can be used without any particular restrictions. It is preferable that the electrolyte has a low resistance to moisture and has an excellent electrolytic solution moisturizing ability. Specifically, porous polymer films, such as polyolefin-based films such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, etc. A porous polymer film made from a polymer or a laminated structure of two or more layers thereof may be used. Further, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc., may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and may optionally be used as a single layer or multilayer structure.

Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries. It is not limited to this.

Specifically, the electrolytic solution may include a non-aqueous organic solvent and a metal salt.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran. , dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl- Aprotic organic solvents such as 2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc. may be used.

In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they have a high dielectric constant as a highly viscous organic solvent and can easily dissociate lithium salt. It is more preferable to use linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, mixed in an appropriate ratio because an electrolytic solution with high electrical conductivity can be produced. can.

As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily dissolved in the nonaqueous electrolyte. For example, the anion of the lithium salt is F ⁻ , Cl ⁻ , I ⁻ , NO ₃ ⁻ , N(CN) ₂ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , (CF ₃ ) ₂ PF ₄ ⁻ , (CF ₃ ) ₃ PF ₃ ⁻ , (CF ₃ ) ₄ PF ₂ ⁻ , (CF ₃ ) ₅ PF ⁻ , (CF ₃ ) ₆ P ⁻ , CF ₃ SO ₃ ⁻ , CF ₃ CF ₂ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (FSO ₂ ) ₂ N ⁻ , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , One or more selected from the group consisting of CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- , and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be used.

In addition to the constituent components of the electrolytic solution, the electrolytic solution may contain, for example, difluoroethylene carbonate, etc., for the purpose of improving battery life characteristics, suppressing decrease in battery capacity, and improving battery discharge capacity. Haloalkylene carbonate compounds, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted One or more additives such as imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride may further be included.

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and therefore can be used in the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. It can be used as a power source for selected medium- and large-sized devices.

Hereinafter, in order to concretely explain the present specification, examples will be given and explained in detail. However, the embodiments according to this specification may be modified into various other forms, and the scope of the present application should not be construed as being limited to the embodiments described below. The Examples of this application are provided so that this disclosure will be thorough and complete, and will fully convey the specification to those skilled in the art.

<Examples and comparative examples>
Example 1
94 g of a powder of Si and SiO ₂ mixed at a molar ratio of 1:1 was mixed in a reactor, and then heated under vacuum at a sublimation temperature of 1,400°C. Thereafter, the vaporized Si and SiO ₂ gas mixture was reacted in a vacuum cooling zone having a cooling temperature of 800° C. and condensed into a solid phase. Next, the coagulated particles were ground for 3 hours using a ball mill to produce particles with a size of 6 μm. Thereafter, while maintaining an inert atmosphere by flowing Ar gas, the particles were placed in the hot zone of the CVD apparatus, and the methane was blown into the hot zone at 900° C. using Ar as a carrier gas. The reaction is carried out at 10 ⁻¹ torr for 5 hours to form a carbon layer on the surface of the particles. Thereafter, 6 g of Li metal powder was added to the particles with the carbon layer formed thereon and mixed, and additional heat treatment was performed at a temperature of 800° C. in an inert atmosphere to produce silicon-based particles containing Li. .

The silicon-based particles and 0.1M HF solution were mixed at a weight ratio of 1:7, stirred for 1 hour, filtered and dried, and then heat-treated at 300°C to produce a negative active material with a LiF layer introduced. .

Example 2
A negative electrode active material was produced in the same manner as in Example 1, except that a 0.15M HF solution was used.

Example 3
A negative electrode active material was produced in the same manner as in Example 1, except that a 0.05M HF solution was used.

Example 4
A negative electrode active material was manufactured in the same manner as in Example 1, except that a 0.2M HF solution was used.

Comparative example 1
A negative electrode active material was manufactured in the same manner as in Example 1 except for the step of introducing the LiF layer.

Comparative example 2
Except that when introducing the LiF layer, the LiF powder and the silicon-based particles were mixed at a weight ratio of 1.5:100, and then the LiF layer was introduced onto the surface of the silicon-based particles using a ball mill. A negative electrode active material was produced in the same manner as in Example 1.

Comparative example 3
Except that when introducing the LiF layer, the LiF powder and the silicon-based particles were mixed at a weight ratio of 0.4:100, and then the LiF layer was introduced onto the surface of the silicon-based particles using a ball mill. A negative electrode active material was produced in the same manner as in Example 1.

<Measurement of carbon layer content>
The content of the carbon layer was analyzed using a CS-analyzer (CS-800, Eltra).

<Measurement of element content and atomic ratio by X-ray photoelectron spectroscopy (XPS)>
The content (at%) and atomic ratio of elements on the surface of the negative electrode active material were confirmed by XPS (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)).

Specifically, a survey scan spectrum and a narrow scan spectrum were obtained for each sample. Next, a survey scan spectrum and a narrow scan spectrum were obtained while performing a depth profile. Depth profiles were performed using monatomic Ar ions for up to 3000 seconds. Measurement and data processing conditions are as follows.

-X-ray source: Monochromated Al K α (1486.6eV)
-X-ray spot size: 400μm
- Sputtering gun: Monatomic Ar (energy: 1000eV, current: low, raster width: 2mm)
-Etching rate: 0.09nm/s for Ta ₂ O ₅
- Operation Mode: CAE (Constant Analyzer Energy) mode
-Survey scan: pass energy 200eV, energy step 1eV
-Narrow scan: scanned mode, pass energy 50eV, energy step 0.1eV
-Charge compensation: flood gun off
-SF:Al THERMO1
-ECF:TPP-2M
-BG subtraction: Shirley

As a result of the above measurements, the content and atomic ratio of each element was calculated based on the total content of the measured elements of 100 at %.

<Measurement of Li content contained in negative electrode active material>
The content of Li atoms was confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (Perkin-Elmer 7300 ICP-OES, AVIO 500).

<LiF content analysis>
20 ml to 200 ml of the sample was taken into a Corning tube and eluted by shaking with 30 g of ultrapure water for 24 hours. At this time, additional dilution was performed as necessary so that the sample concentration fell within the standard calibration curve (1 mg/kg). The F content was measured using IC6000 (Thermo Fisher Scientific) under the following analysis conditions, and the LiF content was calculated from the measured F content.

[Analysis conditions]
-Column: IonPac AS18 (4x250mm), IonPacAG18 (4x50mm)
-Eluent type KOH (30.5mM), Eluent flow rate: 1mL/min
-Detector: Suppressed Conductivity Detector, SRS current: 76mA, Injection volume: 25uL
The compositions of the negative active materials manufactured in the Examples and Comparative Examples are shown in Table 1 below.

<Experiment example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics>
Manufacture of Negative Electrode A mixture of the composite negative electrode active material manufactured in Example 1 and graphite (average particle size (D ₅₀ ): 20 μm) as a carbon-based active material at a weight ratio of 15:85 was used as the negative electrode material.

The negative electrode material, styrene-butadiene rubber (SBR) as a binder, Super C65 as a conductive material, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96:2:1:1 to form a negative electrode slurry. It was added to distilled water as a solvent to produce a negative electrode slurry.

One surface of a copper current collector (thickness: 15 μm) as a negative electrode current collector was coated with the negative electrode slurry at a loading amount of 3.6 mAh/cm ² , rolled, and placed in a vacuum oven at 130° C. for 10 hours. It was dried to form a negative electrode active material layer (thickness: 50 μm), which was used as the negative electrode of Example 1 (negative electrode thickness: 65 μm).

In addition, Examples 2 to 4 were prepared in the same manner as in Example 1, except that the negative electrode active materials of Examples 2 to 4 and Comparative Examples 1 to 3 were used instead of the negative electrode active material of Example 1. And negative electrodes of Comparative Examples 1 to 3 were manufactured.

Manufacturing of secondary battery Lithium metal foil was prepared as a positive electrode.

A porous polyethylene separator was interposed between the negative electrode and the positive electrode of Examples 1 to 4 and Comparative Examples 1 to 3 produced above, and an electrolytic solution was injected. Coin-shaped half cells were each manufactured.

As the electrolytic solution, 0.5% by weight of vinylene carbonate (VC) was dissolved in a solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) mixed at a volume ratio of 7:3, and LiPF ₆ was dissolved at 1M. A solution dissolved at a concentration of was used.

Evaluation of discharge capacity, initial efficiency, and life (capacity maintenance rate) characteristics For the secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 3, discharge capacity, initial efficiency, and cycle capacity retention rate were evaluated.

The cycle capacity retention rate was measured at a temperature of 25°C, and the first cycle and second cycle were charged and discharged at 0.1C, and from the third cycle onwards, charging and discharging was performed at 0.5C (charging and discharging). Conditions: CC/CV, 5mV/0.005C cut-off, discharge conditions: CC, 1.5V cut-off).

Discharge capacity (mAh/g) and initial efficiency (%) were derived from the results of one charge/discharge.

The capacity retention rate was calculated as follows.
Capacity retention rate (%) = {(discharge capacity in Nth cycle)/(discharge capacity in 1st cycle)}×100
(In the above formula, N is an integer of 1 or more.)

The 50th cycle capacity retention rate (%) is shown in Table 2 below.

In Examples 1 to 4, a layer containing LiF is provided on silicon-based particles, the F/O ratio is 0.45 or more, and the F/C ratio is 0.45 or more. 5 or less, and the surface of the silicon-based particles is uniformly coated with a layer containing LiF, which can block the reaction between lithium byproducts and moisture, thereby improving discharge capacity, initial efficiency, and It was confirmed that the capacity retention rate was excellent.

On the other hand, when the LiF layer is not provided on the surface of the silicon-based particles as in Comparative Example 1, the reaction between the lithium by-product of the negative electrode active material and water deteriorates the aqueous slurry processability, which reduces the discharge capacity of the battery. It was confirmed that the initial efficiency and capacity maintenance rate decreased.

In the case of Comparative Example 2, a layer containing LiF was formed on the silicon-based particles, but the F/C ratio was as high as 0.62. As a result, LiF is partially formed thickly, making it difficult to passivate the particles, and lithium by-products are easily exposed, resulting in poor aqueous processability, which reduces the battery's discharge capacity, initial efficiency, and It was confirmed that the capacity retention rate decreased.

In Comparative Example 3, a layer containing LiF was formed on the surface of the silicon-based particles, but the LiF content was small and the F/O ratio was as low as 0.4. As a result, LiF is partially formed on the particles, making it difficult to passivate the particles, and lithium by-products are easily exposed, resulting in poor aqueous processability, which reduces the discharge capacity and initial efficiency of the battery. , and it was confirmed that the capacity retention rate decreased.

Claims (13)

Silicon-based particles containing SiO _x (0<x<2) and a Li compound and provided with a carbon layer on at least a portion of the surface; and a layer containing LiF provided on at least a portion of the silicon-based particles. including,
When analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to O (F/O ratio) is 0.45 or more, and the atomic ratio of F to C (F/C ratio) is 0.5 or less. There is a negative electrode active material. The negative electrode active material according to claim 1, wherein when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to O (F/O ratio) is 0.48 or more and 2 or less. The negative electrode active material according to claim 1, wherein when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of F to C (F/C ratio) is more than 0 and 0.3 or less. The negative electrode active material according to claim 1, wherein the layer containing LiF is included in an amount of 0.5 parts by weight or more and 5 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material. The negative electrode active material according to claim 1, wherein a lithium compound is present between the silicon-based particles and the layer containing LiF. The negative electrode active material according to claim 5, wherein the lithium compound contains one or more selected from the group consisting of _Li2O , _LiOH , and _Li2CO3 . The negative electrode active material according to claim 1, wherein the layer containing LiF is formed by a reaction between HF and _a lithium compound containing one or more selected from the group consisting of _Li2O , LiOH, and _Li2CO3 . The negative electrode active material according to claim 1, wherein Li is contained in an amount of 0.1 to 40 parts by weight based on a total of 100 parts by weight of the negative electrode active material. The negative electrode active material according to claim 1, wherein the carbon layer is included in an amount of 0.1 to 50 parts by weight based on a total of 100 parts by weight of the negative electrode active material. forming silicon-based particles containing SiO _x (0<x<2) and a Li compound and having a carbon layer on at least a portion of the surface; and reacting the silicon-based particles with an HF solution to The method for producing a negative electrode active material according to any one of claims 1 to 9, comprising the step of forming a layer containing LiF on at least a portion of the particles. The step of forming a layer containing LiF on at least a portion of the silicon-based particles by reacting the silicon-based particles with the HF solution includes reacting a lithium compound provided on at least a portion of the silicon-based particles with the HF solution. The method for producing a negative electrode active material according to claim 10, comprising a step of reacting. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 9. A secondary battery comprising the negative electrode according to claim 12.